1.
System of measurement
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A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce, systems of measurement in modern use include the metric system, the imperial system, and United States customary units. The French Revolution gave rise to the system, and this has spread around the world. In most systems, length, mass, and time are base quantities, later science developments showed that either electric charge or electric current could be added to extend the set of base quantities by which many other metrological units could be easily defined. Other quantities, such as power and speed, are derived from the set, for example. Such arrangements were satisfactory in their own contexts, the preference for a more universal and consistent system only gradually spread with the growth of science. Changing a measurement system has substantial financial and cultural costs which must be offset against the advantages to be obtained using a more rational system. However pressure built up, including scientists and engineers for conversion to a more rational. The unifying characteristic is that there was some definition based on some standard, eventually cubits and strides gave way to customary units to met the needs of merchants and scientists. In the metric system and other recent systems, a basic unit is used for each base quantity. Often secondary units are derived from the units by multiplying by powers of ten. Thus the basic unit of length is the metre, a distance of 1.234 m is 1,234 millimetres. Metrication is complete or nearly complete in almost all countries, US customary units are heavily used in the United States and to some degree in Liberia. Traditional Burmese units of measurement are used in Burma, U. S. units are used in limited contexts in Canada due to the large volume of trade, there is also considerable use of Imperial weights and measures, despite de jure Canadian conversion to metric. In the United States, metric units are used almost universally in science, widely in the military, and partially in industry, but customary units predominate in household use. At retail stores, the liter is a used unit for volume, especially on bottles of beverages. Some other standard non-SI units are still in use, such as nautical miles and knots in aviation. Metric systems of units have evolved since the adoption of the first well-defined system in France in 1795, during this evolution the use of these systems has spread throughout the world, first to non-English-speaking countries, and then to English speaking countries
2.
Units of information
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In computing and telecommunications, a unit of information is the capacity of some standard data storage system or communication channel, used to measure the capacities of other systems and channels. In information theory, units of information are used to measure the information contents or entropy of random variables. The most common units are the bit, the capacity of a system which can exist in two states, and the byte, which is equivalent to eight bits. Multiples of these units can be formed from these with the SI prefixes or the newer IEC binary prefixes, information capacity is a dimensionless quantity. In particular, if b is an integer, then the unit is the amount of information that can be stored in a system with N possible states. When b is 2, the unit is the shannon, equal to the content of one bit. A system with 8 possible states, for example, can store up to log28 =3 bits of information, other units that have been named include, Base b =3, the unit is called trit, and is equal to log23 bits. Base b =10, the unit is called decimal digit, hartley, ban, decit, or dit, Base b = e, the base of natural logarithms, the unit is called a nat, nit, or nepit, and is worth log2 e bits. Several conventional names are used for collections or groups of bits, a byte can represent 256 distinct values, such as the integers 0 to 255, or -128 to 127. The IEEE 1541-2002 standard specifies B as the symbol for byte, bytes, or multiples thereof, are almost always used to specify the sizes of computer files and the capacity of storage units. Most modern computers and peripheral devices are designed to manipulate data in whole bytes or groups of bytes, a group of four bits, or half a byte, is sometimes called a nibble or nybble. This unit is most often used in the context of number representations. Computers usually manipulate bits in groups of a size, conventionally called words. The number of bits in a word is defined by the size of the registers in the computers CPU. Some machine instructions and computer number formats use two words, or four words, computer memory caches usually operate on blocks of memory that consist of several consecutive words. These units are customarily called cache blocks, or, in CPU caches, virtual memory systems partition the computers main storage into even larger units, traditionally called pages. Terms for large quantities of bits can be formed using the range of SI prefixes for powers of 10, e. g. kilo =103 =1000, mega- =106 =1000000. These prefixes are often used for multiples of bytes, as in kilobyte, megabyte
3.
Address space
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In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity. For software programs to save and retrieve stored data, each unit of data must have an address where it can be located or else the program will be unable to find. The number of spaces available will depend on the underlying address structure. Address spaces are created by combining enough uniquely identified qualifiers to make an address unambiguous, for a persons physical address, the address space would be a combination of locations, such as a neighborhood, town, city, or country. Some elements of a space may be the same– but if any element in the address is different than addresses in said space will reference different entities. An address space usually provides a partitioning to several regions according to the structure it has. In the case of order, as for memory addresses. Some nested domains hierarchy appears in the case of directed ordered tree as for the Domain Name System or a directory structure, another common feature of address spaces are mappings and translations, often forming numerous layers. This usually means that some higher-level address must be translated to lower-level ones in some way, then, for a disk drive connected via Parallel ATA, each of them must be converted to logical cylinder-head-sector address due to the interface historical shortcomings. It is converted back to LBA by the controller and then, finally, to physical cylinder, head. The Domain Name System maps its names to network-specific addresses, which in turn may be mapped to link layer network addresses via Address Resolution Protocol, also, network address translation may occur on the edge of different IP spaces, such as a local area network and the Internet. An iconic example of virtual-to-physical address translation is virtual memory, where different pages of virtual address space map either to page file or to main memory address space. It is possible that several different virtual addresses all refer to one physical address. It is also possible that a virtual address maps to zero, one. Linear address space Name space Virtualization
4.
Computer memory
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In computing, memory refers to the computer hardware devices involved to store information for immediate use in a computer, it is synonymous with the term primary storage. Computer memory operates at a speed, for example random-access memory, as a distinction from storage that provides slow-to-access program and data storage. If needed, contents of the memory can be transferred to secondary storage. An archaic synonym for memory is store, there are two main kinds of semiconductor memory, volatile and non-volatile. Examples of non-volatile memory are flash memory and ROM, PROM, EPROM and EEPROM memory, most semiconductor memory is organized into memory cells or bistable flip-flops, each storing one bit. Flash memory organization includes both one bit per cell and multiple bits per cell. The memory cells are grouped into words of fixed word length, each word can be accessed by a binary address of N bit, making it possible to store 2 raised by N words in the memory. This implies that processor registers normally are not considered as memory, since they only store one word, typical secondary storage devices are hard disk drives and solid-state drives. In the early 1940s, memory technology oftenly permit a capacity of a few bytes, the next significant advance in computer memory came with acoustic delay line memory, developed by J. Presper Eckert in the early 1940s. Delay line memory would be limited to a capacity of up to a few hundred thousand bits to remain efficient, two alternatives to the delay line, the Williams tube and Selectron tube, originated in 1946, both using electron beams in glass tubes as means of storage. Using cathode ray tubes, Fred Williams would invent the Williams tube, the Williams tube would prove more capacious than the Selectron tube and less expensive. The Williams tube would prove to be frustratingly sensitive to environmental disturbances. Efforts began in the late 1940s to find non-volatile memory, jay Forrester, Jan A. Rajchman and An Wang developed magnetic core memory, which allowed for recall of memory after power loss. Magnetic core memory would become the dominant form of memory until the development of transistor-based memory in the late 1960s, developments in technology and economies of scale have made possible so-called Very Large Memory computers. The term memory when used with reference to computers generally refers to Random Access Memory or RAM, volatile memory is computer memory that requires power to maintain the stored information. Most modern semiconductor volatile memory is either static RAM or dynamic RAM, SRAM retains its contents as long as the power is connected and is easy for interfacing, but uses six transistors per bit. SRAM is not worthwhile for desktop system memory, where DRAM dominates, SRAM is commonplace in small embedded systems, which might only need tens of kilobytes or less. Forthcoming volatile memory technologies that aim at replacing or competing with SRAM and DRAM include Z-RAM and A-RAM, non-volatile memory is computer memory that can retain the stored information even when not powered
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Computer architecture
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In computer engineering, computer architecture is a set of rules and methods that describe the functionality, organization, and implementation of computer systems. Some definitions of architecture define it as describing the capabilities and programming model of a computer, in other definitions computer architecture involves instruction set architecture design, microarchitecture design, logic design, and implementation. The first documented computer architecture was in the correspondence between Charles Babbage and Ada Lovelace, describing the analytical engine, johnson had the opportunity to write a proprietary research communication about the Stretch, an IBM-developed supercomputer for Los Alamos National Laboratory. Brooks went on to develop the IBM System/360 line of computers. Later, computer users came to use the term in many less-explicit ways, the earliest computer architectures were designed on paper and then directly built into the final hardware form. The discipline of architecture has three main subcategories, Instruction Set Architecture, or ISA. The ISA defines the code that a processor reads and acts upon as well as the word size, memory address modes, processor registers. Microarchitecture, or computer organization describes how a processor will implement the ISA. The size of a computers CPU cache for instance, is an issue that generally has nothing to do with the ISA, system Design includes all of the other hardware components within a computing system. These include, Data processing other than the CPU, such as memory access Other issues such as virtualization, multiprocessing. There are other types of computer architecture, E. g. the C, C++, or Java standards define different Programmer Visible Macroarchitecture. UISA —a group of machines with different hardware level microarchitectures may share a common microcode architecture, pin Architecture, The hardware functions that a microprocessor should provide to a hardware platform, e. g. the x86 pins A20M, FERR/IGNNE or FLUSH. Also, messages that the processor should emit so that external caches can be invalidated, pin architecture functions are more flexible than ISA functions because external hardware can adapt to new encodings, or change from a pin to a message. The term architecture fits, because the functions must be provided for compatible systems, the purpose is to design a computer that maximizes performance while keeping power consumption in check, costs low relative to the amount of expected performance, and is also very reliable. For this, many aspects are to be considered which includes Instruction Set Design, Functional Organization, Logic Design, the implementation involves Integrated Circuit Design, Packaging, Power, and Cooling. Optimization of the design requires familiarity with Compilers, Operating Systems to Logic Design, an instruction set architecture is the interface between the computers software and hardware and also can be viewed as the programmers view of the machine. Computers do not understand high level languages such as Java, C++, a processor only understands instructions encoded in some numerical fashion, usually as binary numbers. Software tools, such as compilers, translate those high level languages into instructions that the processor can understand, besides instructions, the ISA defines items in the computer that are available to a program—e. g
6.
Power of two
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In mathematics, a power of two means a number of the form 2n where n is an integer, i. e. the result of exponentiation with number two as the base and integer n as the exponent. In a context where only integers are considered, n is restricted to values, so we have 1,2. Because two is the base of the numeral system, powers of two are common in computer science. Written in binary, a power of two always has the form 100…000 or 0. 00…001, just like a power of ten in the decimal system, a word, interpreted as an unsigned integer, can represent values from 0 to 2n −1 inclusively. Corresponding signed integer values can be positive, negative and zero, either way, one less than a power of two is often the upper bound of an integer in binary computers. As a consequence, numbers of this show up frequently in computer software. For example, in the original Legend of Zelda the main character was limited to carrying 255 rupees at any time. Powers of two are used to measure computer memory. A byte is now considered eight bits (an octet, resulting in the possibility of 256 values, the prefix kilo, in conjunction with byte, may be, and has traditionally been, used, to mean 1,024. However, in general, the term kilo has been used in the International System of Units to mean 1,000, binary prefixes have been standardized, such as kibi meaning 1,024. Nearly all processor registers have sizes that are powers of two,32 or 64 being most common, powers of two occur in a range of other places as well. For many disk drives, at least one of the size, number of sectors per track. The logical block size is almost always a power of two. Numbers that are not powers of two occur in a number of situations, such as video resolutions, but they are often the sum or product of two or three powers of two, or powers of two minus one. For example,640 =512 +128 =128 ×5, put another way, they have fairly regular bit patterns. A prime number that is one less than a power of two is called a Mersenne prime, for example, the prime number 31 is a Mersenne prime because it is 1 less than 32. Similarly, a number that is one more than a positive power of two is called a Fermat prime—the exponent itself is a power of two. A fraction that has a power of two as its denominator is called a dyadic rational, the numbers that can be represented as sums of consecutive positive integers are called polite numbers, they are exactly the numbers that are not powers of two
7.
International Electrotechnical Commission
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The IEC also manages three global conformity assessment systems that certify whether equipment, system or components conform to its International Standards. The first International Electrical Congress took place in 1881 at the International Exposition of Electricity, at that time the International System of Electrical and Magnetic Units was agreed to. The IEC was instrumental in developing and distributing standards for units of measurement, particularly Gauss, Hertz and it also first proposed a system of standards, the Giorgi System, which ultimately became the SI, or Système International d’unités. In 1938, it published a multilingual international vocabulary to unify terminology relating to electrical, electronic and this effort continues, and the International Electrotechnical Vocabulary remains an important work in the electrical and electronic industries. The CISPR – in English, the International Special Committee on Radio Interference – is one of the groups founded by the IEC, originally located in London, the commission moved to its current headquarters in Geneva in 1948. It has regional centres in Asia-Pacific, Latin America and North America, today, the IEC is the worlds leading international organization in its field, and its standards are adopted as national standards by its members. The work is done by some 10,000 electrical and electronics experts from industry, government, academia, test labs, IEC standards have numbers in the range 60000–79999 and their titles take a form such as IEC60417, Graphical symbols for use on equipment. Following the Dresden Agreement with CENELEC the numbers of older IEC standards were converted in 1997 by adding 60000, for example IEC27 became IEC60027. Standards of the 60000 series are also preceded by EN to indicate that the IEC standard is also adopted by CENELEC as a European standard. The IEC cooperates closely with the International Organization for Standardization and the International Telecommunication Union, Standards developed jointly with ISO such as ISO/IEC26300, ISO/IEC27001, and CASCO ISO/IEC17000 series, carry the acronym of both organizations. The use of the ISO/IEC prefix covers publications from ISO/IEC Joint Technical Committee 1 - Information Technology, as well as conformity assessment standards developed by ISO CASCO, other standards developed in cooperation between IEC and ISO are assigned numbers in the 80000 series, such as IEC 82045-1. IEC standards are also being adopted by other certifying bodies such as BSI, CSA, UL & ANSI/INCITS, SABS, SAI, SPC/GB, IEC standards adopted by other certifying bodies may have some noted differences from the original IEC standard. The IEC is made up of members, called national committees, national committees are constituted in different ways. Some NCs are public sector only, some are a combination of public and private sector, about 90% of those who prepare IEC standards work in industry
8.
Institute of Electrical and Electronics Engineers
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The Institute of Electrical and Electronics Engineers is a professional association with its corporate office in New York City and its operations center in Piscataway, New Jersey. It was formed in 1963 from the amalgamation of the American Institute of Electrical Engineers, today, it is the worlds largest association of technical professionals with more than 400,000 members in chapters around the world. Its objectives are the educational and technical advancement of electrical and electronic engineering, telecommunications, computer engineering, IEEE stands for the Institute of Electrical and Electronics Engineers. The association is chartered under this full legal name, IEEEs membership has long been composed of engineers and scientists. For this reason the organization no longer goes by the name, except on legal business documents. The IEEE is dedicated to advancing technological innovation and excellence and it has about 430,000 members in about 160 countries, slightly less than half of whom reside in the United States. The major interests of the AIEE were wire communications and light, the IRE concerned mostly radio engineering, and was formed from two smaller organizations, the Society of Wireless and Telegraph Engineers and the Wireless Institute. After World War II, the two became increasingly competitive, and in 1961, the leadership of both the IRE and the AIEE resolved to consolidate the two organizations. The two organizations merged as the IEEE on January 1,1963. The IEEE is incorporated under the Not-for-Profit Corporation Law of the state of New York and it was formed in 1963 by the merger of the Institute of Radio Engineers and the American Institute of Electrical Engineers. The IEEE serves as a publisher of scientific journals and organizer of conferences, workshops. IEEE develops and participates in activities such as accreditation of electrical engineering programs in institutes of higher learning. The IEEE logo is a design which illustrates the right hand grip rule embedded in Benjamin Franklins kite. IEEE has a dual complementary regional and technical structure – with organizational units based on geography and it manages a separate organizational unit which recommends policies and implements programs specifically intended to benefit the members, the profession and the public in the United States. The IEEE includes 39 technical Societies, organized around specialized technical fields, the IEEE Standards Association is in charge of the standardization activities of the IEEE. The IEEE History Center became an organization to the Engineering. The new ETHW is an effort by various engineering societies as a formal repository of topic articles, oral histories, first-hand histories, Landmarks + Milestones. The IEEE History Center is annexed to Stevens University Hoboken, NJ, in 2016, the IEEE acquired GlobalSpec, adding the provision of engineering data for a profit to its organizational portfolio
9.
IBM 7030 Stretch
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The IBM7030, also known as Stretch, was IBMs first transistorized supercomputer. Even though the 7030 was much slower than expected, it was the fastest computer in the world from 1961 until the first CDC6600 became operational in 1964, PC World magazine named Stretch as one of the biggest project management failures in IT history. In spite of Stretchs failure to meet its own goals, it served as the basis for many of the design features of the successful IBM System/360. The project lead, Stephen W. Dunwell, was blackballed for his role in the failure. In early 1955, Dr. Edward Teller of the University of California Radiation Laboratory wanted a new scientific computing system for three-dimensional hydrodynamic calculations, proposals were requested from IBM and UNIVAC for this new system, to be called Livermore Automatic Reaction Calculator or LARC. According to IBM executive Cuthbert Hurd, such a system would cost roughly $2.5 million, delivery was to be two to three years after the contract was signed. At IBM, a team at Poughkeepsie including John Griffith. Just after they finished and were about to present the proposal, Ralph Palmer stopped them and said, the proposed design would have been built with either point-contact transistors or surface-barrier transistors, both likely to be soon outperformed by the then newly invented diffusion transistor. Livermore was not impressed, and in May 1955 they announced that UNIVAC had won the LARC contract, LARC would eventually be delivered in June 1960. In January 1956, Project Stretch was formally initiated, in November 1956, IBM won the contract with the aggressive performance goal of a speed at least 100 times the IBM704. In 1960, the price of $13.5 million was set for the IBM7030, in 1961, actual benchmarks indicated that the performance of the IBM7030 was only about 30 times the IBM704, causing considerable embarrassment for IBM. In May 1961, Tom Watson announced a cut of all 7030s under negotiation to $7.78 million. Its floating-point addition time was 1. 38-1.5 microseconds, multiplication time was 2. 48-2.70 microseconds, while the IBM7030 was not considered successful, it spawned many technologies incorporated in future machines that were highly successful. The IBM7302 Model I Core Storage units were used in the IBM7090, IBM7070. Multiprogramming, memory protection, generalized interrupts, the eight-bit byte for I/O were all concepts later incorporated in the IBM System/360 line of computers as well as most later CPUs. By 1966 he had received an apology and been made an IBM Fellow, the 7030 CPU used emitter-coupled logic on 18 types of Standard Modular System cards. It used 4,025 double cards and 18,747 single cards, holding 169,100 transistors and it used high-speed NPN and PNP germanium drift transistors, with cut-off frequency over 100 MHz, and using ~50mW each. Some third level circuits used a 3rd voltage level, each logic level has a delay of about 20 nS
10.
Biting
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Biting is a common behaviour which involves the opening and closing of the jaw found in many animals. This behaviour is found in reptiles, mammals, fish and amphibians, animal bites often result in serious infections and mortality. Dog bites are commonplace, with children the most commonly bitten, biting is also an age appropriate behavior and reaction for human children 30 months and younger. Conversely, children above this age are expected to have verbal skills to explain their needs and dislikes, biting may be prevented by methods including redirection, changing the environment and responding to biting by talking about appropriate ways to express anger and frustration. School age children, those older than 30 months, who habitually bite may require professional help, some discussion of human biting appears in The Kinsey Report on Sexual Behavior in the Human Female. Bite force quotient Chewing The Bite Fight
11.
MIT Lincoln Laboratory
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Research and development activities focus on long-term technology development as well as rapid system prototyping and demonstration. These efforts are aligned within key mission areas, the laboratory works with industry to transition new concepts and technology for system development and deployment. The laboratory also maintains several field sites around the world, the laboratorys inception was prompted by the Air Defense Systems Engineering Committees 1950 report that concluded the United States was unprepared for the threat of an air attack. S. Air Force suggested that MIT could provide the research needed to develop an air defense that could detect, identify, james R. Killian, then president of MIT, was not eager for MIT to become involved in air defense. He asked the Air Force if MIT could first conduct a study to evaluate the need for a new laboratory, killians proposal was approved, and a study named Project Charles was carried out between February and August 1951. The Semi-Automatic Ground Environment Air Defense System is the beginning of MIT Lincoln Laboratorys history of developing innovative technology, the system was conceived to meet the challenge of providing air defense to the continental United States. SAGE was designed to collect, analyze, and finally relay data from a multitude of radars, the key to this system was a computer that could perform reliably in real time. MITs Whirlwind computer, built in the 1940s, looked to be a candidate for the system. However, the Whirlwind was not reliable or fast enough for the processing needed for analyzing data coming in from dozens of, perhaps even 100, the magnetic core memory revolutionized computing. Computers became machines that were not just large and fast calculators, industry followed this development closely, adopting the magnetic core memory that expanded the capabilities of computers. Lincoln Laboratory quickly established a reputation for pioneering advanced electronics in air defense systems, many of the technical developments that later evolved into improved systems for the airborne detection and tracking of aircraft and ground vehicles have formed the basis for current research. Lincoln Laboratory conducts research and development pertinent to national security on behalf of the services, the Office of the Secretary of Defense. Projects focus on the development and prototyping of new technologies and capabilities, program activities extend from fundamental investigations, through simulation and analysis, to design and field testing of prototype systems. Emphasis is placed on transitioning technology to industry, the dissemination of information to the government, academia, and industry is a principal focus of Lincoln Laboratorys technical mission. Wide dissemination of information is achieved through annual technical workshops, seminars. Current news about Laboratory technical milestones is featured on the laboratorys website, MIT Lincoln Laboratory maintains a strong relationship with the MIT campus. Approximately 1700 technical staff members work on research, prototype building, the technical staff come from a broad range of scientific and engineering fields, with electrical engineering, physics, computer science and mathematics being among the most prevalent. Two-thirds of the staff hold advanced degrees, and 60% of those degrees are at the doctoral level
12.
RAND Corporation
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RAND Corporation is an American nonprofit global policy think tank originally formed by Douglas Aircraft Company to offer research and analysis to the United States Armed Forces. It is financed by the U. S. government and private endowment, corporations including the health industry, universities. The organization has expanded to work with governments, private foundations, international organizations. Rich is president and chief officer of the RAND Corporation. Its American locations include, Santa Monica, California, Arlington, Virginia, Pittsburgh, Pennsylvania, the RAND Gulf States Policy Institute has an office in New Orleans, Louisiana. RAND Europe is located in Cambridge, United Kingdom, and Brussels, RAND Australia is located in Canberra, Australia. RAND is home to the Frederick S. Pardee RAND Graduate School, one of the eight original programs in public policy. The program aims to have value in that students work with RAND analysts on real-world problems. The campus is at RANDs Santa Monica research facility, the Pardee RAND School is the worlds largest PhD-granting program in policy analysis. Unlike many other universities, all Pardee RAND Graduate School students receive fellowships to cover their education costs and this allows them to dedicate their time to engage in research projects and provides them on-the-job training. RAND also offers a number of internship and fellowship programs allowing students, most of these projects are short-term and are worked on independently with the mentoring of a RAND staff member. RAND publishes the RAND Journal of Economics, a journal of economics. Thirty-two recipients of the Nobel Prize, primarily in the fields of economics and physics, have involved or associated with RAND at some point in their career. General Henry H. Arnold, commander of the United States Army Air Forces, in March 1946 Douglas Aircraft Company was granted the contract to research on intercontinental warfare by adopting operations research. In May 1946 the Preliminary Design of an Experimental World-Circling Spaceship was released, initial capital for the split was provided by the Ford Foundation. On October 1,1945, Project RAND was set up under special contract to the Douglas Aircraft Company and began operations in December 1945, chief strategist Herman Kahn also posited the idea of a winnable nuclear exchange in his 1960 book On Thermonuclear War. This led to Kahn being one of the models for the character of the film Dr. Strangelove. RAND was incorporated as an organization to further promote scientific, educational
13.
Binary-coded decimal
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In computing and electronic systems, binary-coded decimal is a class of binary encodings of decimal numbers where each decimal digit is represented by a fixed number of bits, usually four or eight. Special bit patterns are used for a sign or for other indications. The precise 4-bit encoding may vary however, for technical reasons, the ten states representing a BCD decimal digit are sometimes called tetrades with those dont care-states unused named pseudo-tetrads or pseudo-decimal digit). BCDs principal drawbacks are an increase in the complexity of the circuits needed to implement basic arithmetics. BCD was used in many early computers, and is implemented in the instruction set of machines such as the IBM System/360 series and its descendants. BCD takes advantage of the fact that any one decimal numeral can be represented by a four bit pattern, the most obvious way of encoding digits is natural BCD, where each decimal digit is represented by its corresponding four-bit binary value, as shown in the following table. This is also called 8421 encoding, other encodings are also used, including so-called 4221 and 7421 — named after the weighting used for the bits — and excess-3. For example, the BCD digit 6, 0110b in 8421 notation, is 1100b in 4221, 0110b in 7421, Packed, Two numerals are encoded into a single byte, with one numeral in the least significant nibble and the other numeral in the most significant nibble. To represent numbers larger than the range of a single byte any number of contiguous bytes may be used, also note how packed BCD is more efficient in storage usage as compared to unpacked BCD, encoding the same number in unpacked format would consume twice the storage. Shifting and masking operations are used to pack or unpack a packed BCD digit, other logical operations are used to convert a numeral to its equivalent bit pattern or reverse the process. BCD is very common in systems where a numeric value is to be displayed, especially in systems consisting solely of digital logic. By employing BCD, the manipulation of data for display can be greatly simplified by treating each digit as a separate single sub-circuit. This matches much more closely the reality of display hardware—a designer might choose to use a series of separate identical seven-segment displays to build a metering circuit. If the numeric quantity were stored and manipulated as pure binary, therefore, in cases where the calculations are relatively simple, working throughout with BCD can lead to a simpler overall system than converting to and from binary. Most pocket calculators do all their calculations in BCD, the same argument applies when hardware of this type uses an embedded microcontroller or other small processor. Often, smaller code results when representing numbers internally in BCD format, for these applications, some small processors feature BCD arithmetic modes, which assist when writing routines that manipulate BCD quantities. In Packed BCD, each of the two nibbles of each byte represent a decimal digit, Packed BCD has been in use since at least the 1960s and is implemented in all IBM mainframe hardware since then. Most implementations are big endian, i. e. with the more significant digit in the half of each byte
14.
United States Army
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The United States Armed Forces are the federal armed forces of the United States. They consist of the Army, Marine Corps, Navy, Air Force, from the time of its inception, the military played a decisive role in the history of the United States. A sense of unity and identity was forged as a result of victory in the First Barbary War. Even so, the Founders were suspicious of a permanent military force and it played an important role in the American Civil War, where leading generals on both sides were picked from members of the United States military. Not until the outbreak of World War II did a standing army become officially established. The National Security Act of 1947, adopted following World War II and during the Cold Wars onset, the U. S. military is one of the largest militaries in terms of number of personnel. It draws its personnel from a pool of paid volunteers. As of 2016, the United States spends about $580.3 billion annually to fund its military forces, put together, the United States constitutes roughly 40 percent of the worlds military expenditures. For the period 2010–14, the Stockholm International Peace Research Institute found that the United States was the worlds largest exporter of major arms, the United States was also the worlds eighth largest importer of major weapons for the same period. The history of the U. S. military dates to 1775 and these forces demobilized in 1784 after the Treaty of Paris ended the War for Independence. All three services trace their origins to the founding of the Continental Army, the Continental Navy, the United States President is the U. S. militarys commander-in-chief. Rising tensions at various times with Britain and France and the ensuing Quasi-War and War of 1812 quickened the development of the U. S. Navy, the reserve branches formed a military strategic reserve during the Cold War, to be called into service in case of war. Time magazines Mark Thompson has suggested that with the War on Terror, Command over the armed forces is established in the United States Constitution. The sole power of command is vested in the President by Article II as Commander-in-Chief, the Constitution also allows for the creation of executive Departments headed principal officers whose opinion the President can require. This allowance in the Constitution formed the basis for creation of the Department of Defense in 1947 by the National Security Act, the Defense Department is headed by the Secretary of Defense, who is a civilian and member of the Cabinet. The Defense Secretary is second in the chain of command, just below the President. Together, the President and the Secretary of Defense comprise the National Command Authority, to coordinate military strategy with political affairs, the President has a National Security Council headed by the National Security Advisor. The collective body has only power to the President
15.
United States Navy
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The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U. S. Navy is the largest, most capable navy in the world, the U. S. Navy has the worlds largest aircraft carrier fleet, with ten in service, two in the reserve fleet, and three new carriers under construction. The service has 323,792 personnel on duty and 108,515 in the Navy Reserve. It has 274 deployable combat vessels and more than 3,700 operational aircraft as of October 2016, the U. S. Navy traces its origins to the Continental Navy, which was established during the American Revolutionary War and was effectively disbanded as a separate entity shortly thereafter. It played a role in the American Civil War by blockading the Confederacy. It played the role in the World War II defeat of Imperial Japan. The 21st century U. S. Navy maintains a global presence, deploying in strength in such areas as the Western Pacific, the Mediterranean. The Navy is administratively managed by the Department of the Navy, the Department of the Navy is itself a division of the Department of Defense, which is headed by the Secretary of Defense. The Chief of Naval Operations is an admiral and the senior naval officer of the Department of the Navy. The CNO may not be the highest ranking officer in the armed forces if the Chairman or the Vice Chairman of the Joint Chiefs of Staff. The mission of the Navy is to maintain, train and equip combat-ready Naval forces capable of winning wars, deterring aggression, the United States Navy is a seaborne branch of the military of the United States. The Navys three primary areas of responsibility, The preparation of naval forces necessary for the prosecution of war. The development of aircraft, weapons, tactics, technique, organization, U. S. Navy training manuals state that the mission of the U. S. Armed Forces is to prepare and conduct prompt and sustained combat operations in support of the national interest, as part of that establishment, the U. S. Navys functions comprise sea control, power projection and nuclear deterrence, in addition to sealift duties. It follows then as certain as that night succeeds the day, that without a decisive naval force we can do nothing definitive, the Navy was rooted in the colonial seafaring tradition, which produced a large community of sailors, captains, and shipbuilders. In the early stages of the American Revolutionary War, Massachusetts had its own Massachusetts Naval Militia, the establishment of a national navy was an issue of debate among the members of the Second Continental Congress. Supporters argued that a navy would protect shipping, defend the coast, detractors countered that challenging the British Royal Navy, then the worlds preeminent naval power, was a foolish undertaking. Commander in Chief George Washington resolved the debate when he commissioned the ocean-going schooner USS Hannah to interdict British merchant ships, and reported the captures to the Congress
16.
ASCII
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ASCII, abbreviated from American Standard Code for Information Interchange, is a character encoding standard. ASCII codes represent text in computers, telecommunications equipment, and other devices, most modern character-encoding schemes are based on ASCII, although they support many additional characters. ASCII was developed from telegraph code and its first commercial use was as a seven-bit teleprinter code promoted by Bell data services. Work on the ASCII standard began on October 6,1960, the first edition of the standard was published in 1963, underwent a major revision during 1967, and experienced its most recent update during 1986. Compared to earlier telegraph codes, the proposed Bell code and ASCII were both ordered for more convenient sorting of lists, and added features for other than teleprinters. Originally based on the English alphabet, ASCII encodes 128 specified characters into seven-bit integers as shown by the ASCII chart above. The characters encoded are numbers 0 to 9, lowercase letters a to z, uppercase letters A to Z, basic punctuation symbols, control codes that originated with Teletype machines, for example, lowercase j would become binary 1101010 and decimal 106. ASCII includes definitions for 128 characters,33 are non-printing control characters that affect how text and space are processed and 95 printable characters, of these, the IANA encourages use of the name US-ASCII for Internet uses of ASCII. The ASA became the United States of America Standards Institute and ultimately the American National Standards Institute, there was some debate at the time whether there should be more control characters rather than the lowercase alphabet. The X3.2.4 task group voted its approval for the change to ASCII at its May 1963 meeting, the X3 committee made other changes, including other new characters, renaming some control characters and moving or removing others. ASCII was subsequently updated as USAS X3. 4-1967, then USAS X3. 4-1968, ANSI X3. 4-1977 and they proposed a 9-track standard for magnetic tape, and attempted to deal with some punched card formats. The X3.2 subcommittee designed ASCII based on the earlier teleprinter encoding systems, like other character encodings, ASCII specifies a correspondence between digital bit patterns and character symbols. This allows digital devices to communicate each other and to process, store. Before ASCII was developed, the encodings in use included 26 alphabetic characters,10 numerical digits, ITA2 were in turn based on the 5-bit telegraph code Émile Baudot invented in 1870 and patented in 1874. The committee debated the possibility of a function, which would allow more than 64 codes to be represented by a six-bit code. In a shifted code, some character codes determine choices between options for the character codes. It allows compact encoding, but is reliable for data transmission. The standards committee decided against shifting, and so ASCII required at least a seven-bit code, the committee considered an eight-bit code, since eight bits would allow two four-bit patterns to efficiently encode two digits with binary-coded decimal
17.
IBM System/360
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The IBM System/360 is a mainframe computer system family that was announced by IBM on April 7,1964, and delivered between 1965 and 1978. It was the first family of computers designed to cover the range of applications, from small to large. The design made a distinction between architecture and implementation, allowing IBM to release a suite of compatible designs at different prices. The launch of the System/360 family introduced IBMs Solid Logic Technology, the slowest System/360 model announced in 1964, the Model 30, could perform up to 34,500 instructions per second, with memory from 8 to 64 KB. The 1967 IBM System/360 Model 91 could do up to 16.6 million instructions per second, up to 8 megabytes of slower Large Capacity Storage was also available. Many consider the one of the most successful computers in history. The chief architect of System/360 was Gene Amdahl, and the project was managed by Fred Brooks, the commercial release was piloted by another of Watsons lieutenants, John R. Opel, who managed the launch of IBM’s System 360 mainframe family in 1964. Application level compatibility for System/360 software is maintained to present day with the System z servers, contrasting with at-the-time normal industry practice, IBM created an entire series of computers, from small to large, low to high performance, all using the same instruction set. This feat allowed customers to use a model and then upgrade to larger systems as their needs increased without the time. This flexibility greatly lowered barriers to entry, with other vendors, customers had to choose between machines they could outgrow and machines that were potentially overpowered. This meant that many simply did not buy computers. IBM initially announced a series of six computers and forty common peripherals, IBM eventually delivered fourteen models, including rare one-off models for NASA. The initial announcement in 1964 included Models 30,40,50,60,62, the first three were low- to middle-range systems aimed at the IBM1400 series market. All three first shipped in mid-1965, the last three, intended to replace the 7000 series machines, never shipped and were replaced by the 65 and 75, which were first delivered in November 1965, and January 1966, respectively. Later additions to the low-end included models 20,22, and 25, the Model 20 had several sub-models, sub-model 5 was at the higher end of the model. A succession of high-end machines included the Model 67,85,91,95, the 85 design was intermediate between the System/360 line and the follow-on System/370 and was the basis for the 370/165. There was a System/370 version of the 195, but it did not include Dynamic Address Translation, the implementations differed substantially, using different native data path widths, presence or absence of microcode, yet were extremely compatible. Except where specifically documented, the models were architecturally compatible, the 91, for example, was designed for scientific computing and provided out-of-order instruction execution, but lacked the decimal instruction set used in commercial applications
18.
AT&T
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AT&T Inc. is an American multinational telecommunications conglomerate, headquartered at Whitacre Tower in downtown Dallas, Texas. AT&T is the third-largest company in Texas, as of February 2017, AT&T is the 12th largest company in the world as measured by a composite of revenues, profits, assets and market valuation. AT&T is the largest telecommunications company in the world by revenue, as of 2017, it is also the 18th-largest mobile telecom operator in the world, with 135 million mobile customers. AT&T was ranked at #4 on the 2017 rankings of the worlds most valuable brands published by Brand Finance, Southwestern Bell changed its name to SBC Communications Inc. in 1995. In 2005, SBC purchased former parent AT&T Corp. and took on its branding, with the merged entity naming itself AT&T Inc. and using the iconic AT&T Corp. logo and stock-trading symbol. The current AT&T reconstitutes much of the former Bell System and includes ten of the original 22 Bell Operating Companies, AT&T can trace its origin back to the original Bell Telephone Company founded by Alexander Graham Bell after his invention of the telephone. This monopoly was known as the Bell System, and during this period, for periods of time, the former AT&T was the worlds largest phone company. In 1982, U. S. regulators broke up the AT&T monopoly, requiring AT&T to divest its regional subsidiaries and these new companies were known as Regional Bell Operating Companies, or more informally, Baby Bells. AT&T continued to long distance services, but as a result of this breakup, faced competition from new competitors such as MCI. Southwestern Bell was one of the created by the breakup of AT&T. The architect of divestiture for Southwestern Bell was Robert G. Pope, the company soon started a series of acquisitions. This includes the 1987 acquisition of Metromedia mobile business, and the acquisition of several companies in the early 1990s. In the later half of the 1990s, the company acquired several other companies, including some Baby Bells. During this time, the changed its name to SBC Communications. By 1998, the company was in the top 15 of the Fortune 500, in 2005, SBC purchased AT&T for $16 billion. After this purchase, SBC adopted the better-known AT&T name and brand, the current AT&T claims the original AT&Ts history as its own, though its corporate structure only dates from 1983. It also retains SBCs pre-2005 stock price history, in September 2013, AT&T announced it would expand into Latin America through a collaboration with Carlos Slims América Móvil. In December 2013, AT&T announced plans to sell its Connecticut wireline operations to Stamford-based Frontier Communications, in July 2015, AT&T purchased DirecTV for $48.5 billion, or $67.1 billion including assumed debt
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Telephony
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The history of telephony is intimately linked to the invention and development of the telephone. The term is used frequently to refer to computer hardware, software, and computer network systems. In this context the technology is referred to as Internet telephony. The first telephones were connected directly in pairs, each user had a separate telephone wired to the locations he might wish to reach. This quickly became inconvenient and unmanageable when people wanted to communicate with more than a few people, the inventions of the telephone exchange provided the solution for establishing telephone connections with any other telephone in service in the local area. Each telephone was connected to the exchange via one wire pair, nearby exchanges in other service areas were connected with trunk lines and long distance service could be established by relaying the calls through multiple exchanges. Initially the switchboards were manually operated by an attendant, a switchboard operator, when a customer cranked a handle on the telephone, it turned on an indicator on the board in front of the operator who would plug the operator headset into that jack and offer service. The caller had to ask for the party by name, later by number. If the called station answered the operator disconnected their headset and completed the station-to-station circuit, trunk calls were made with the assistance of other operators at other exchangers in the network. In modern times, most telephones are plugged into telephone jacks, the jacks are connected by inside wiring to a drop wire which connects the building to a cable. Cables usually bring a number of drop wires from all over a district access network to one wire center or telephone exchange. Most of the exchanges in the world are interconnected through a system of larger switching systems, today, telephony uses digital technology in the provisioning of telephone services and systems. This advancement has reduced costs in communication, and improved the quality of voice services, the first implementation of this, ISDN, permitted all data transport from end-to-end speedily over telephone lines. This service was made much less important due to the ability to provide digital services based on the IP protocol. The integration of software and computer systems is a major development in the evolution of the automated office. The term is used in describing the services of call centers. Its also sometimes used to describe the ability to use your personal computer to initiate, CTI is not a new concept and has been used in the past in large telephone networks, but only dedicated call centers could justify the costs of the required equipment installation. Dialed Number Identification Service on a scale is wide enough for its implementation to bring value to business or residential telephone usage
20.
Microprocessor
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A microprocessor is a computer processor which incorporates the functions of a computers central processing unit on a single integrated circuit, or at most a few integrated circuits. Microprocessors contain both combinational logic and sequential digital logic, Microprocessors operate on numbers and symbols represented in the binary numeral system. The integration of a whole CPU onto a chip or on a few chips greatly reduced the cost of processing power. Integrated circuit processors are produced in numbers by highly automated processes resulting in a low per unit cost. Single-chip processors increase reliability as there are many electrical connections to fail. As microprocessor designs get better, the cost of manufacturing a chip generally stays the same, before microprocessors, small computers had been built using racks of circuit boards with many medium- and small-scale integrated circuits. Microprocessors combined this into one or a few large-scale ICs, the internal arrangement of a microprocessor varies depending on the age of the design and the intended purposes of the microprocessor. Advancing technology makes more complex and powerful chips feasible to manufacture, a minimal hypothetical microprocessor might only include an arithmetic logic unit and a control logic section. The ALU performs operations such as addition, subtraction, and operations such as AND or OR, each operation of the ALU sets one or more flags in a status register, which indicate the results of the last operation. The control logic retrieves instruction codes from memory and initiates the sequence of operations required for the ALU to carry out the instruction, a single operation code might affect many individual data paths, registers, and other elements of the processor. As integrated circuit technology advanced, it was feasible to manufacture more and more complex processors on a single chip, the size of data objects became larger, allowing more transistors on a chip allowed word sizes to increase from 4- and 8-bit words up to todays 64-bit words. Additional features were added to the architecture, more on-chip registers sped up programs. Floating-point arithmetic, for example, was not available on 8-bit microprocessors. Integration of the point unit first as a separate integrated circuit and then as part of the same microprocessor chip. Occasionally, physical limitations of integrated circuits made such practices as a bit slice approach necessary, instead of processing all of a long word on one integrated circuit, multiple circuits in parallel processed subsets of each data word. With the ability to put large numbers of transistors on one chip and this CPU cache has the advantage of faster access than off-chip memory, and increases the processing speed of the system for many applications. Processor clock frequency has increased more rapidly than external memory speed, except in the recent past, a microprocessor is a general purpose system. Several specialized processing devices have followed from the technology, A digital signal processor is specialized for signal processing, graphics processing units are processors designed primarily for realtime rendering of 3D images
21.
Intel 8008
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The Intel 8008 is an early byte-oriented microprocessor designed and manufactured by Intel and introduced in April 1972. It was an 8-bit CPU with an external 14-bit address bus that could address 16 KB of memory, originally known as the 1201, the chip was commissioned by Computer Terminal Corporation to implement an instruction set of their design for their Datapoint 2200 programmable terminal. As the chip was delayed and did not meet CTCs performance goals, an agreement permitted Intel to market the chip to other customers after Seiko expressed an interest in using it for a calculator. CTC formed in San Antonio in 1968 under the direction of Austin O. Gus Roche and Phil Ray, Roche, in particular, was primarily interested in producing a desktop computer. However, given the immaturity of the market, the business plan mentioned only a Teletype Model 33 ASR replacement. The case was designed to fit in the same space as an IBM Selectric typewriter. Although commercially successful, the 3300 had ongoing problems due to the amount of circuitry packed into such a small space. In order to address the heating and other issues, a re-design started that featured the CPU part of the internal circuitry re-implemented on a single chip, looking for a company able to produce their chip design, Roche turned to Intel, then primarily a vendor of memory chips. Roche met with Bob Noyce, who expressed concern with the concept, John Frassanito recalls that Noyce said it was an idea, and that Intel could do it. He said that if you have a chip, you can only sell one chip per computer, while with memory. Nevertheless, Noyce agreed to a $50,000 development contract in early 1970, texas Instruments was also brought in as a second supplier. TI was able to make samples of the 1201 based on Intel drawings, CTC decided to re-implement the new version of the terminal using discrete TTL instead of waiting for a single chip CPU. The new system was released as the Datapoint 2200 in the spring 1970, CTC paused development of the 1201 after the 2200 was released, as it was no longer needed. By that point CTC had once again moved on, this time to the Datapoint 2200 II, the 1201 was no longer powerful enough for the new model. CTC voted to end their involvement with the 1201, leaving the designs intellectual property to Intel instead of paying the $50,000 contract, Intel renamed it the 8008, and put it in their catalog in April 1972 priced at $120. Intels initial worries about their existing customer base leaving them proved unfounded, and this was followed by the Intel 8080, and then the hugely successful Intel x86 family. One of the first teams to build a system around the 8008 was Bill Pentz team at California State University. The project started in the spring of 1972 and with key help from Tektronix the system was fully functional a year later, Bill assisted Intel with the MCS-8 kit and provided key input to the Intel 8080 instruction set which helped make it useful for the industry and hobbyists
22.
Intel 8080
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The Intel 8080 was the second 8-bit microprocessor designed and manufactured by Intel and was released in April 1974. It was an extended and enhanced variant of the earlier 8008 design, a slightly faster variant 8080A-1 became available later with clock frequency limit up to 3.125 MHz. The 8080 was successful enough that compatibility at the language level became a design requirement for the 8086 when design for it was started in 1976. This also means that the 8080 indirectly influenced the ubiquitous 32-bit and 64-bit x86 architectures of today, the Intel 8080 was the successor to the 8008. It used the basic instruction set and register model as the 8008. Every instruction in the 8008 has an equivalent instruction in the 8080, the 8080 also added a few 16-bit operations to its instruction set as well. Whereas the 8008 required the use of the HL register pair to indirectly access its 14-bit memory space, in addition, the internal 7-level push-down call stack of the 8008 was replaced by a dedicated 16-bit stack pointer register. The 8080s large 40-pin DIP packaging permitted it to provide a 16-bit address bus and it also has a 16-bit stack pointer to memory, and a 16-bit program counter. The processor maintains internal flag bits which indicates the results of arithmetic, conditional branch instructions test the various flag status bits. The flags can be copied as a group to the accumulator, the A accumulator and the flags together are called the PSW register or program status word. As with many other 8-bit processors, all instructions are encoded in a single byte, some of them are followed by one or two bytes of data, which can be an immediate operand, a memory address, or a port number. Like larger processors, it has automatic CALL and RET instructions for multi-level procedure calls and returns, there are also eight one-byte call instructions for subroutines located at the fixed addresses 00h, 08h, 10h. and 38h. These were intended to be supplied by external hardware in order to invoke a corresponding interrupt-service routine, the most sophisticated command is XTHL, which is used for exchanging the register pair HL with the value stored at the address indicated by the stack pointer. Most 8-bit operations can only be performed on the 8-bit accumulator, for 8-bit operations with two operands, the other operand can be either an immediate value, another 8-bit register, or a memory byte addressed by the 16-bit register pair HL. Direct copying is supported between any two 8-bit registers and between any 8-bit register and an HL-addressed memory byte, due to the regular encoding of the MOV instruction, there are redundant codes to copy a register into itself, which were of little use, except for delays. However, what would have been a copy from the HL-addressed cell into itself is used to encode the halt instruction. The XCHG instruction exchanges the values of the HL and DE register pairs, by adding HL to itself, it is possible to achieve the same result as a 16-bit arithmetical left shift with one instruction. The 8080 supported up to 256 input/output ports, accessed via dedicated I/O instructions—taking port addresses as operands and this I/O mapping scheme was regarded as an advantage, as it freed up the processors limited address space
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Intel 8086
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The 8086 is a 16-bit microprocessor chip designed by Intel between early 1976 and mid-1978, when it was released. The 8086 gave rise to the x86 architecture which eventually became Intels most successful line of processors, in 1972, Intel launched the 8008, the first 8-bit microprocessor. It implemented a set designed by Datapoint corporation with programmable CRT terminals in mind. The device needed several additional ICs to produce a computer, in part due to it being packaged in a small 18-pin memory package. Two years later, Intel launched the 8080, employing the new 40-pin DIL packages originally developed for calculator ICs to enable a separate address bus and it had an extended instruction set that was source compatible with the 8008 and also included some 16-bit instructions to make programming easier. Other well known 8-bit microprocessors that emerged during these years were Motorola 6800, General Instrument PIC16X, MOS Technology 6502, Zilog Z80, the 8086 project started in May 1976 and was originally intended as a temporary substitute for the ambitious and delayed iAPX432 project. It was an attempt to draw attention from the less-delayed 16- and 32-bit processors of other manufacturers and at the time to counter the threat from the Zilog Z80. The programming model and instruction set was based on the 8080 in order to make this possible, however, the 8086 design was expanded to support full 16-bit processing, instead of the fairly basic 16-bit capabilities of the 8080/8085. Instructions directly supporting nested ALGOL-family languages such as Pascal and PL/M were also added, according to principal architect Stephen P. Morse, this was a result of a more software centric approach than in the design of earlier Intel processors. Other enhancements included microcoded multiply and divide instructions and a bus structure better adapted to future coprocessors, the 8086 took a little more than two years from idea to working product, which was considered rather fast for a complex design in 1976–1978. The 8086 was sequenced using a mixture of random logic and microcode and was implemented using depletion-load nMOS circuitry with approximately 20,000 active transistors and it was soon moved to a new refined nMOS manufacturing process called HMOS that Intel originally developed for manufacturing of fast static RAM products. This was followed by HMOS-II, HMOS-III versions, and, eventually, the original chip measured 33 mm² and minimum feature size was 3.2 μm. The architecture was defined by Stephen P. Morse with some help, logic designer Jim McKevitt and John Bayliss were the lead engineers of the hardware-level development team and Bill Pohlman the manager for the project. All internal registers, as well as internal and external buses, are 16 bits wide. A 20-bit external address bus provides a 1 MB physical address space and this address space is addressed by means of internal memory segmentation. The data bus is multiplexed with the bus in order to fit all of the control lines into a standard 40-pin dual in-line package. It provides a 16-bit I/O address bus, supporting 64 KB of separate I/O space, the maximum linear address space is limited to 64 KB, simply because internal address/index registers are only 16 bits wide. Programming over 64 KB memory boundaries involves adjusting the segment registers, some of the control pins, which carry essential signals for all external operations, have more than one function depending upon whether the device is operated in min or max mode
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Nibble
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In computing, a nibble is a four-bit aggregation, or half an octet. It is also known as half-byte or tetrade, in a networking or telecommunication context, the nibble is often called a semi-octet, quadbit, or quartet. A nibble has sixteen possible values, a nibble can be represented by a single hexadecimal digit and called a hex digit. A full byte is represented by two digits, therefore, it is common to display a byte of information as two nibbles. Sometimes the set of all 256 byte values is represented as a 16×16 table, four-bit computer architectures use groups of four bits as their fundamental unit. Such architectures were used in microprocessors, pocket calculators and pocket computers. They continue to be used in some microcontrollers, the term nibble originates from its representing half a byte, with byte a homophone of the English word bite. The alternative spelling nybble reflects the spelling of byte, as noted in editorials of Kilobaud, another early recorded use of the term nybble was in 1977 within the consumer-banking technology group at Citibank. It created a pre-ISO8583 standard for transactional messages between cash machines and Citibanks data centers that used the basic informational unit NABBLE, the nibble is used to describe the amount of memory used to store a digit of a number stored in packed decimal format within an IBM mainframe. This technique is used to make faster and debugging easier. An 8-bit byte is split in half and each nibble is used to one decimal digit. The last nibble of the variable is reserved for the sign, thus a variable which can store up to nine digits would be packed into 5 bytes. Ease of debugging resulted from the numbers being readable in a hex dump where two hex numbers are used to represent the value of a byte, as 16×16 =28, for example, a five-byte BCD value of 31415926 5C represents a decimal value of +314159265. Historically, there are cases where nybble was used for a group of bits greater than 4, in the Apple II microcomputer line, much of the disk drive control and group-coded recording was implemented in software. Writing data to a disk was done by converting 256-byte pages into sets of 5-bit nibbles, moreover,1982 documentation for the Integrated Woz Machine refers consistently to an 8 bit nibble. The term byte once had the same ambiguity and meant a set of bits but not necessarily 8, hence the distinction of bytes and octets or of nibbles and quartets. Today, the terms byte and nibble almost always refer to 8-bit and 4-bit collections respectively and are rarely used to express any other sizes. The terms semi-nibble or nibblet have occasionally used to refer to half a nibble
25.
Hexadecimal
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In mathematics and computing, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, Hexadecimal numerals are widely used by computer system designers and programmers. As each hexadecimal digit represents four binary digits, it allows a more human-friendly representation of binary-coded values, one hexadecimal digit represents a nibble, which is half of an octet or byte. For example, a byte can have values ranging from 00000000 to 11111111 in binary form. In a non-programming context, a subscript is typically used to give the radix, several notations are used to support hexadecimal representation of constants in programming languages, usually involving a prefix or suffix. The prefix 0x is used in C and related languages, where this value might be denoted as 0x2AF3, in contexts where the base is not clear, hexadecimal numbers can be ambiguous and confused with numbers expressed in other bases. There are several conventions for expressing values unambiguously, a numerical subscript can give the base explicitly,15910 is decimal 159,15916 is hexadecimal 159, which is equal to 34510. Some authors prefer a text subscript, such as 159decimal and 159hex, or 159d and 159h. example. com/name%20with%20spaces where %20 is the space character, thus ’, represents the right single quotation mark, Unicode code point number 2019 in hex,8217. In the Unicode standard, a value is represented with U+ followed by the hex value. Color references in HTML, CSS and X Window can be expressed with six hexadecimal digits prefixed with #, white, CSS allows 3-hexdigit abbreviations with one hexdigit per component, #FA3 abbreviates #FFAA33. *nix shells, AT&T assembly language and likewise the C programming language, to output an integer as hexadecimal with the printf function family, the format conversion code %X or %x is used. In Intel-derived assembly languages and Modula-2, hexadecimal is denoted with a suffixed H or h, some assembly languages use the notation HABCD. Ada and VHDL enclose hexadecimal numerals in based numeric quotes, 16#5A3#, for bit vector constants VHDL uses the notation x5A3. Verilog represents hexadecimal constants in the form 8hFF, where 8 is the number of bits in the value, the Smalltalk language uses the prefix 16r, 16r5A3 PostScript and the Bourne shell and its derivatives denote hex with prefix 16#, 16#5A3. For PostScript, binary data can be expressed as unprefixed consecutive hexadecimal pairs, in early systems when a Macintosh crashed, one or two lines of hexadecimal code would be displayed under the Sad Mac to tell the user what went wrong. Common Lisp uses the prefixes #x and #16r, setting the variables *read-base* and *print-base* to 16 can also used to switch the reader and printer of a Common Lisp system to Hexadecimal number representation for reading and printing numbers. Thus Hexadecimal numbers can be represented without the #x or #16r prefix code, MSX BASIC, QuickBASIC, FreeBASIC and Visual Basic prefix hexadecimal numbers with &H, &H5A3 BBC BASIC and Locomotive BASIC use & for hex. TI-89 and 92 series uses a 0h prefix, 0h5A3 ALGOL68 uses the prefix 16r to denote hexadecimal numbers, binary, quaternary and octal numbers can be specified similarly
